Memory cells including dielectric materials, memory devices including the memory cells, and methods of forming same

ABSTRACT

A memory cell comprising a threshold switching material over a first electrode on a substrate. The memory cell includes a second electrode over the threshold switching material and at least one dielectric material between the threshold switching material and at least one of the first electrode and the second electrode. A memory material overlies the second electrode. The dielectric material may directly contact the threshold switching material and each of the first electrode and the second electrode. Memory cells including only one dielectric material between the threshold switching material and an electrode are disclosed. A memory device including the memory cells and methods of forming the memory cells are also described.

TECHNICAL FIELD

Embodiments disclosed herein relate to memory devices providing improvedelectrical properties, and methods of forming such devices. Morespecifically, embodiments disclosed herein relate to memory devicesincluding memory cells with dielectric materials between electrodes andthreshold switching materials to improve device performance, and methodsof forming such memory cells and memory devices.

BACKGROUND

Conventional memory cells are configured to read and write data byapplying a voltage to a memory material. A voltage is applied to thememory material through electrodes coupled to each end of the memorycell. The memory material is set to a particular resistance stateaccording to an amount of current applied by the electrodes. Theresistance state of the memory material may be used to distinguish alogic value of the memory cell.

In addition to the memory material, a conventional memory cell may alsoinclude an isolation element (e.g., a switch, a select device, etc.)configured to be reversibly electrically switched from a resistive stateto a conductive state. Within a conventional memory device, a pluralityof memory cells is positioned between a plurality of access lines (e.g.,word lines) and a plurality of digit lines (e.g., bit lines). A singlecell is selected for reading and writing by applying a voltage betweenthe access line and the digit line associated with a particular memorycell. Including the isolation element impairs or, ideally, prevents,residual voltages from affecting the physical state (e.g., theresistance) of non-selected memory cells.

Threshold switching materials are currently considered favorableisolation elements, such as in, for example, cross-point architecturememory cells. At a threshold voltage, the threshold switching materialchanges to an electrically conductive state, allowing current to flowthrough the threshold switching material. Below the threshold voltage,the threshold switching material is in a resistive state, limitingleakage current flow through the threshold switching material.

The threshold switching material may be formed between a pair ofelectrodes of the memory cell, through which current flows to and fromthe threshold switching material. Conventional threshold switchingmaterials include materials that undesirably react with the materials ofthe electrodes surrounding the threshold switching materials. Thethreshold switching materials often react with the materials that formthe electrodes. In addition, the threshold switching material maydiffuse into the electrode and materials from the electrode may diffuseinto the threshold switching material, forming a discontinuous interfacebetween the electrodes and the threshold switching material. Forexample, this diffusion of materials occurs in conventional memory cellsat an interface between a metal electrode and an amorphous siliconthreshold switching material, or at an interface between a carbonelectrode and a chalcogenide threshold switching material.

Disadvantageously, however, these reactions between the thresholdswitching material and the surrounding electrodes cause electricaldefects at the interface between the threshold switching material andthe electrodes, reducing the electrical quality of the switch and theassociated memory cell. For example, the poor interface may cause aphenomenon known as Fermi level pinning, which often increases thethreshold voltage of each memory cell, increases the threshold voltagevariability across individual memory cells within a memory array,increases the leakage current through the threshold switching materialat sub-threshold voltages, and reduces the useful lifetime of theswitch.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B are simplified cross-sectional views of a memorycell including dielectric materials adjacent a threshold switchingmaterial according to some embodiments of the present disclosure;

FIG. 2A and FIG. 2B are simplified cross-sectional views of a memorycell including a dielectric material on one side of a thresholdswitching material according to other embodiments of the presentdisclosure;

FIG. 3A and FIG. 3B are simplified cross-sectional views of anothermemory cell including a dielectric material on one side of a thresholdswitching material according to yet other embodiments of the presentdisclosure;

FIG. 4 is a simplified cross-sectional view of a memory cell includingdielectric materials adjacent a threshold switching material accordingto some embodiments of the present disclosure;

FIG. 5 is a simplified cross-sectional view of another memory cellincluding a dielectric material on one side of a threshold switchingmaterial according to other embodiments of the present disclosure;

FIG. 6 is a simplified cross-sectional view of another memory cellincluding a dielectric material on one side of a threshold switchingmaterial according to yet other embodiments of the present disclosure;

FIG. 7 is a perspective view of a memory cell array including aplurality of memory cells of the present disclosure;

FIG. 8 is a cross-sectional view of a memory device in accordance withan embodiment of the present disclosure;

FIG. 9A through FIG. 9E are cross-sectional views illustrating differentprocess stages for a method of forming the memory device of FIG. 8;

FIG. 10 is a graphical representation comparing the threshold voltagevariability of the memory cells of the present disclosure toconventional memory cells; and

FIG. 11A through FIG. 11D are graphical representations comparing deviceperformance of a memory cell of the present disclosure to a conventionalmemory cell.

DETAILED DESCRIPTION

The illustrations included herewith are not meant to be actual views ofany particular systems or memory structures, but are merely idealizedrepresentations that are employed to describe embodiments herein.Elements and features common between figures may retain the samenumerical designation except that, for ease of following thedescription, for the most part, reference numerals begin with the numberof the drawing on which the elements are introduced or most fullydiscussed.

The following description provides specific details, such as materialtypes, material thicknesses, and processing conditions in order toprovide a thorough description of embodiments described herein. However,a person of ordinary skill in the art will understand that theembodiments disclosed herein may be practiced without employing thesespecific details. Indeed, the embodiments may be practiced inconjunction with conventional fabrication techniques employed in thesemiconductor industry. In addition, the description provided hereindoes not describe the formation of a complete process flow formanufacturing memory cells, and the structures described below do notform a complete semiconductor device. Only those process acts andstructures necessary to understand the embodiments described herein aredescribed in detail below. Additional acts to form a complete asemiconductor device including the structures described herein may beperformed by conventional techniques.

In some embodiments disclosed herein, a dielectric material between athreshold switching material (e.g., a material that may be used in anisolation element such as a select device or an access device) and anelectrode may improve device performance of a memory cell. Thedielectric material may be positioned between the threshold switchingmaterial and the electrode and may reduce the number of electricaldefects at an interface of the threshold switching material with othermaterials (e.g., the electrodes) of the memory cell. The dielectricmaterial may increase the probability that each memory cell in a memoryarray has a threshold voltage closer to the average threshold voltage ofthe memory cells in the memory array compared to conventional memorycells in conventional memory arrays, decrease the threshold voltage ofthe memory cells in the memory array, and increase the number of cycleseach memory cell may undergo while remaining stable.

According to embodiments disclosed herein, the dielectric material maybe formed in cross-point memory cells. The memory cells may be comprisedof various materials, depending on the desired function of the finaldevice. The dielectric material may be formed between the thresholdswitching material and an electrode adjacent the threshold switchingmaterial. In other embodiments, the dielectric material is formedbetween the threshold switching material and each of the adjacentelectrodes. In some embodiments, the threshold switching material is indirect contact with the dielectric material and the dielectric materialseparates the threshold switching material from the electrodes adjacentthe threshold switching material.

Referring to FIG. 1A, a memory cell 101 may include a first electrode106 (e.g., a bottom electrode), a first dielectric material 108 over thefirst electrode 106, a threshold switching material 110 over the firstdielectric material 108, a second dielectric material 112 over thethreshold switching material 110, a second electrode 114 (e.g., a middleelectrode) over the second dielectric material 112, a memory material116 over the second electrode 114, and a third electrode 118 (e.g., atop electrode) over the memory material 116. The memory cell 101 may becoupled to access lines, such as a word line 104 which may underlie thefirst electrode 106 and a digit line 120 (e.g., a bit line) which mayoverlie the third electrode 118. The memory material 116 may beelectrically coupled to the threshold switching material 110 through themiddle electrode 114.

The word line 104 may include any suitable material including, but notlimited to, a conductive material such as a metal, a metal alloy, aconductive metal oxide, or combinations thereof. For example, the wordline 104 may be formed from tungsten (W), tungsten nitride (WN), nickel(Ni), tantalum nitride (TaN), platinum (Pt), gold (Au), titanium nitride(TiN), titanium silicon nitride (TiSiN), titanium aluminum nitride(TiAlN), molybdenum nitride (MoN), or a combination thereof. In at leastsome embodiments, the word line 104 is formed from tungsten. The wordline 104 may be formed in, on, or over a substrate (not shown) usingconventional techniques, such as atomic layer deposition (ALD), chemicalvapor deposition (CVD), plasma enhanced chemical vapor deposition(PECVD), low pressure chemical vapor deposition (LPCVD), physical vapordeposition (PVD), or other film deposition processes. PVD includes, butis not limited to, sputtering, evaporation, or ionized PVD. Suchdeposition techniques are known in the art and, therefore, are notdescribed in detail herein.

The substrate may be in the form of a semiconductor substrate, a basesemiconductor layer on a supporting structure, a metal electrode, or asemiconductor substrate having one or more layers, structures, orregions formed thereon. The substrate may be a conventional siliconsubstrate or other bulk substrate including a layer of semiconductivematerial. The substrate may include, but is not limited to, silicon,silicon-on-insulator (“SOI”) substrates, silicon-on-sapphire (“SOS”)substrates, and silicon-on-glass (“SOG”), epitaxial silicon on a basesemiconductor foundation, or another semiconductor or optoelectronicmaterial, such as silicon-germanium, germanium, gallium arsenide,gallium nitride, and indium phosphide. The substrate may be doped orundoped.

The first electrode 106 may be formed from a conductive material with asufficiently high melting point such that the first electrode 106 doesnot melt during normal operation of the memory cell 101. As used herein,a material with a high melting point means and includes a material witha melting point above about 1,800° C. Conventional memory cells mayrequire that the electrode be substantially non-reactive with thethreshold switching material 110. However, in embodiments of the presentdisclosure, since the dielectric material (e.g., the first dielectricmaterial 108 and the second dielectric material 112) is positionedbetween the threshold switching material 110 and at least one of thefirst electrode 106 and the second electrode 114, reactions between theelectrodes and the threshold switching material 110 may be reduced oreliminated. Thus, the material of the first electrode 106 may bereactive or substantially inert (e.g., non-reactive) with the thresholdswitching material 110. Accordingly, the electrodes 106, 114 may beformed from a broader range of materials compared to conventional memorycells.

The first electrode 106 may be formed from a conductivecarbon-containing material. For example, the first electrode 106 may beformed from carbon (C) atoms, a compound including carbon atoms, such asa carbon nitride, titanium carbon nitride (TiC_(x)N_(y)), tantalumcarbon nitride (TaC_(x)N_(y)), titanium silicon carbon nitride(TiSiC_(x)N_(y)), titanium aluminum carbon nitride (TiAlC_(x)N_(y)),titanium silicon aluminum carbon nitride (TiSiAlC_(x)N_(y)), tungstencarbon nitride (WC_(x)N_(y)), tantalum carbon oxynitride(TaCO_(x)N_(y)), and tungsten silicon carbon nitride (WSiC_(x)N_(y))), acarbon-containing metal silicide, tungsten, titanium, platinum,ruthenium, ruthenium oxide (RuO_(x)), metal nitrides (such as tungstennitride (WN_(x)), titanium nitride (TiN_(x)), tantalum nitride(TaN_(x)), titanium aluminum nitride (TiAl_(x)N_(y))), and combinationsthereof, wherein x is between about 0 and about 6.0 and y is betweenabout 0 and about 6.0. In some embodiments, the first electrode 106includes a conductive carbon-containing material with a high meltingpoint and a threshold voltage that is similar to a threshold voltage ofthe threshold switching material 110. In some embodiments, the firstelectrode 106 is a carbon electrode.

The first electrode 106 may be configured to conduct current to thethreshold switching material 110. The thickness of the first electrode106 may be selected at least partially based on material characteristicsof one or more other components of the memory cell 101 (e.g., the memorymaterial 116, the second electrode 114, the threshold switching material110, etc.). For example, the thickness of the first electrode 106 mayenable a threshold voltage of the first electrode 106 (e.g., a voltageat which the first electrode 106 functions as a low resistanceconductor) to be substantially close to a threshold voltage of thethreshold switching material 110 (described below). The thickness of thefirst electrode 106 may be between about 30 Å and about 2,000 Å, such asbetween about 100 Å and about 1,500 Å. In some embodiments, thethickness of the first electrode is about 200 Å.

The first electrode 106 may be formed on the word line 104 byconventional techniques including, but not limited to, ALD, CVD, PECVD,LPCVD, and PVD. In one embodiment, the first electrode 106 is formed byPVD, so that the first electrode 106 has high film quality, as well ashigh thermal compatibility with the threshold switching material 110. Byway of non-limiting example, a carbon source, such as graphite, and insome embodiments, a source of an optional material to be co-sputteredwith the carbon may be provided in a deposition chamber (not shown),such as a PVD chamber. The PVD chamber may be configured to generate aplasma including a noble gas element (e.g., helium, neon, argon,krypton, xenon, or radon). In at least one embodiment, the plasmaincludes argon. As the carbon source and the source of the optionalmaterial are bombarded with the plasma, carbon atoms and atoms of theoptional material are sputtered from a surface of the sources and formedon a surface of the word line 104. A desired thickness of the firstelectrode 106 may be achieved by controlling a deposition time and anamount of power used.

The first dielectric material 108 may be formed over the first electrode106 and located between the first electrode 106 and the thresholdswitching material 110 to reduce or prevent the threshold switchingmaterial 110 from reacting with the first electrode 106. The firstdielectric material 108 may hinder elements of the threshold switchingmaterial 110 from diffusing into the first electrode 106 and may alsohinder elements of the first electrode 106 from diffusing into thethreshold switching material 110. Thus, the memory cell 101 may includea dielectric material on at least one side of the threshold switchingmaterial 110. The first dielectric material 108 may be between thethreshold switching material 110 and the first electrode 106. In someembodiments, the first dielectric material 108 is formed over and incontact with a metal material of the first electrode 106.

The first dielectric material 108 may be forming between (e.g.,intervene between) the first electrode 106 and the threshold switchingmaterial 110. The first dielectric material 108 may directly contacteach of the first electrode 106 and the threshold switching material110. In some embodiments, the first dielectric material 108 is in directcontact with the threshold switching material 110 and another material(not shown) intervenes between the first dielectric material 108 and thefirst electrode 106.

The first dielectric material 108 may form a distinct boundary betweenthe first electrode 106 and the first dielectric material 108 and adistinct boundary between the first dielectric material 108 and thethreshold switching material 110, providing a reduced number ofelectrical defects at interfaces of the threshold switching material 110with other materials as compared to conventional memory cells.

The first dielectric material 108 may include any dielectric materialwith a high melting point that is chemically unreactive with each of thethreshold switching material 110 and the first electrode 106. The firstdielectric material 108 may include high-k metal oxides such asrefractory metal oxides, an oxynitride such as SiO_(x)N_(y), wherein xis between about 1 and about 4 and y is between about 1 and about 4,aluminum oxynitride (AlO_(x)N_(y), wherein x is between about 0 andabout 1.0 and y is between about 0 and about 1.0), nitrides (e.g.,silicon nitride, aluminum nitride, hafnium nitride, zirconium nitride,etc.), carbon oxynitride (CN_(x)O_(y), wherein x is between about 0about 1.0 and y is between about 0 and about 1.0), and combinationsthereof.

By way of non-limiting example, the first dielectric material 108 mayinclude aluminum oxide (AlO_(x)), a compound including aluminum,silicon, and oxygen (aluminum silicon oxide (AlSi_(x)O_(y))), magnesiumoxide (MgO_(x)), strontium oxide (SrO), barium oxide (BaO), lanthanumoxide (LaO_(x)), lutetium oxide (LuO_(x)), dysprosium scandium oxide(DySc_(y)O_(x)), strontium titanium oxide (SrTiO₃, also known as STO),aluminum oxynitride (AlO_(x)N_(y)), a refractory metal oxide, such ashafnium oxide (HfO_(x)), iridium oxide (IrO_(x)), titanium oxide(TiO_(x)), tantalum oxide (Ta_(x)O₅, such as Ta₂O₅), zirconium oxide(ZrO₂), niobium oxide (Nb_(x)O_(y), such as NbO, NbO₂, or Nb₂O₅),molybdenum oxide, a refractory metal alloy oxide, such as hafniumoxynitride (HfO_(x)N_(y)) and hafnium silicon oxide (HfSi_(x)O_(y)), andcombinations thereof, wherein x is between about 0 and about 6.0 and yis between about 0 and about 6.0. As used herein, the term “refractorymetal alloy oxide” means and includes a compound including a refractorymetal, oxygen, and at least one other element. The at least one otherelement may be another refractory metal. Other high-k dielectricmaterials may be utilized depending on the end use of the semiconductordevice. In some embodiments, the first dielectric material 108 is analuminum oxide, such as Al₂O₃. In other embodiments, the firstdielectric material 108 includes more than one dielectric material, suchas a first portion of a high-k dielectric material and a second portionof another high-k dielectric material.

The first dielectric material 108 may, optionally, be doped withcomponents such as oxygen, sulfur, carbon, fluorine, metallic elements(e.g., transition metals), and combinations thereof. In someembodiments, the first dielectric material 108 is doped with at leastone of silver, nickel, gallium, germanium, arsenic, indium, tin,antimony, gold, lead, bismuth, tantalum, zirconium, hafnium, andniobium. The concentration of the dopant in the first dielectricmaterial 108 may be higher or lower at the interface with the thresholdswitching material 110 than at the side opposite this interface. In someembodiments, the concentration of the dopant may be uniform within thefirst dielectric material 108. However, the first dielectric material108 may include a gradient of the dopant, such as at least a portionthat is doped and another portion that is undoped.

A thickness of the first dielectric material 108 may be sufficient tocover exposed portions of the first electrode 106. However, thethickness of the first dielectric material 108 may not be so thick thatthe first dielectric material 108 exhibits tunneling characteristics.The first dielectric material 108 may be substantially continuousbetween the first electrode 106 and the threshold switching material 110such that the first electrode 106 does not physically contact thethreshold switching material 110. Thus, the first dielectric material108 may physically isolate the first electrode 106 from the thresholdswitching material 110. However, the first dielectric material 108 maybe discontinuous as long as the first electrode 106 does not physicallycontact the threshold switching material 110. The thickness of the firstdielectric material 108 may be between about 3 Å and about 50 Å, such asbetween about 3 Å and about 5 Å, between about 5 Å and about 10 Å,between about 10 Å and about 20 Å, between about 20 Å and about 30 Å, orbetween about 30 Å and about 50 Å. In some embodiments, the thickness ofthe first dielectric material 108 is 10 Å. In some embodiments, thefirst dielectric material 108 includes only one monolayer of the firstdielectric material 108.

The first dielectric material 108 may be fox using conventionaltechniques, such as ALD, CVD, PECVD, LPCVD, PVD, or other filmdeposition processes, which are not described herein. In someembodiments, the first dielectric material 108 is formed by ALD.

The threshold switching material 110 may be formed from any knownmaterial configured to be reversibly electrically switched (i.e.,configured to reversibly electrically switch or change) from arelatively resistive state to a relatively conductive state and havingsubstantially no tendency to undergo a structural or phase change undernormal operating conditions of the memory cell 101. For example,subjecting the threshold switching material 110 to a voltage above acritical threshold level may switch or change the threshold switchingmaterial 110 from the relatively resistive state to the relativelyconductive state. The relatively conductive state may continue until acurrent passing through the threshold switching material 110 drops belowa critical holding level, at which time the threshold switching material110 may switch or change to the relatively resistive state. When in therelatively resistive state, the threshold switching material 110 may beconfigured to impair or prevent residual voltages from word lines 104and digit lines 120 associated with another memory cell 101 fromaffecting the physical state of the memory cell 101 associated with thethreshold switching material 110.

By way of non-limiting example, the threshold switching material 110 maybe a chalcogenide compound. As used herein, the term “chalcogenidecompound” refers to a binary or multinary compound that includes atleast one chalcogen atom and at least one more electropositive elementor radical. As used herein, the term “chalcogen” refers to an element ofGroup VI of the Periodic Table, such as oxygen (O), sulfur (S), selenium(Se), tellurium (Te), or polonium (Po). The electropositive element mayinclude, but is not limited to, nitrogen (N), silicon (Si), nickel (Ni),gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), indium (In),tin (Sn), antimony (Sb), gold (Au), lead (Pb), bismuth (Bi), orcombinations thereof. The chalcogenide compound may be a binary, ternaryalloy, quaternary, quinary, senary, or a septenary alloy.

By way of non-limiting example, the threshold switching material 110 maybe a chalcogenide compound including the chalcogen and theelectropositive element. The chalcogen may be at least one of O, S, Se,Te, or Po. The electropositive element may include, but is not limitedto, N, Si, Ni, Ga, Ge, As, Ag, In, Cd, Zn, Sn, Sb, Au, Pb, Bi, Cr, Nb,Pd, Pt, or combinations thereof. Non-limiting examples of chalcogenidecompounds suitable for use as the threshold switching material 110include Si, As, Se compounds; As and Te compounds, such as As₂Te₃; Asand Se compounds, such as As₂Se₃; As, Te, and Ge compounds, such asAs₃₀Te₄₅Ge₂₅; As, Se, and Ge compounds, such as As₂₈Se₄₂Ge₃₀; As, S, Se,and Ge compounds, such as As30S₁₂Se₃₃Ge₂₅; and As, Te, Ge, Si, and Incompounds, such as As₃₇Te₃₉Ge₉Si₁₄In. In at least some embodiments, thethreshold switching material 110 is As₃₇Te₃₉Ge₉Si₁₄In. In otherembodiments, the threshold switching material 110 includes arsenic,selenium, silicon, and germanium.

The threshold switching material 110 may be formed over the firstelectrode 106 and may be disposed between the first electrode 106 andthe middle electrode 114. The threshold switching material 110 may beformed using conventional techniques, such as ALD, CVD, PECVD, LPCVD,and PVD, which are not described in detail herein. The thresholdswitching material 110 may be fainted at higher deposition temperatures(e.g., up to approximately 400° C.) without reacting with the firstelectrode 106 because of the presence of the first dielectric material108. The threshold switching material 110 may be formed over the firstelectrode 106 without reacting with the first electrode 106 because thefirst dielectric material 108 may foil a barrier between the thresholdswitching material 110 and the first electrode 106.

The second dielectric material 112 may overlie the threshold switchingmaterial 110. The second dielectric material 112 may be formed between(e.g., intervene between) the threshold switching material 110 and thesecond electrode 114. The second dielectric material 112 may directlycontact each of the threshold switching material 110 and the secondelectrode 114. In some embodiments, the second dielectric material 112is in direct contact with the threshold switching material 110 andanother material (not shown) intervenes between the second dielectricmaterial 112 and the second electrode 114.

The second dielectric material 112 may reduce or prevent interactionsbetween the threshold switching material 110 and the second electrode114. The second dielectric material 112 may act as a diffusion barrierand may reduce diffusion of elements of the threshold switching material110 into the second electrode 114 and may also reduce diffusion ofelements of the second electrode 114 into the threshold switchingmaterial 110.

The second dielectric material 112 may be formed from any dielectricmaterial with a high melting point that is chemically unreactive witheach of the threshold switching material 110 and the second electrode114. The second dielectric material 112 may be formed from one of thematerials described above for the first dielectric material 108. Thesecond dielectric material 112 may be fainted from the same material asthe first dielectric material 112 or may be formed from a differentmaterial. In some embodiments, the second dielectric material 112includes a dielectric material that is different than the firstdielectric material 110. In some embodiments, the second dielectricmaterial 112 includes an aluminum oxide, such as Al₂O₃.

The second dielectric material 112 may form a distinct boundary betweenthe threshold switching material 110 and the second dielectric material112 and a distinct boundary between the second dielectric material 112and the second electrode 114, resulting in a reduced number ofelectrical defects at interfaces of the threshold switching material 110with other materials as compared to conventional memory cells.

The second dielectric material 112 may, optionally, be doped withcomponents such as oxygen, sulfur, carbon, fluorine, metallic elements(e.g., transition metals), and combinations thereof, similar to thedopants of the first dielectric material 108, as described above.

A thickness of the second dielectric material 112 may be sufficient tocover exposed portions of the threshold switching material 110. However,the thickness of the second dielectric material 112 may not be so thickthat the second dielectric material 112 exhibits tunnelingcharacteristics. The second dielectric material 112 may be substantiallycontinuous between the threshold switching material 110 and the secondelectrode 114 such that the threshold switching material 110 does notphysically contact the second electrode 114. Thus, the second dielectricmaterial 112 may physically isolate the threshold switching material 110from the second electrode 114. However, the second dielectric material112 may be discontinuous as long as the threshold switching material 110does not physically contact the second electrode 114. The thickness ofthe second dielectric material 112 may be between about 3 Å and about 50Å, such as between about 3 Å and about 5 Å, between about 5 Å and about10 Å, between about 10 Å and about 20 Å, between about 20 Å and about 30Å, or between about 30 Å and about 50 Å. In some embodiments, thethickness of the second dielectric material 112 is 10 Å. The thicknessof the second dielectric material 112 may be greater than, less than, orequal to the thickness of the first dielectric material 108. In someembodiments, the second dielectric material 112 includes only onemonolayer of the second dielectric material 112.

The second dielectric material 112 may be formed using conventionaltechniques, such as ALD, CVD, PECVD, LPCVD, PVD, or other filmdeposition processes, which are not described herein. In someembodiments, the second dielectric material 112 is formed by ALD. Thesecond electrode 114 may be forming over the second dielectric material112 at higher deposition temperatures (e.g., up to approximately 400°C.) without reacting with the threshold switching material 110 becauseof the presence of the second dielectric material 112.

Each of the first dielectric material 108 and the second dielectricmaterial 112 may be formed between an electrode and the thresholdswitching material 110. The first dielectric material 108 and the seconddielectric material 112 may be formed in a direction perpendicular to adirection of current flow through the memory cell 101. For example,current may flow through the memory cell 101 between the word line 104and the digit line 120. The first dielectric material 108 and the seconddielectric material 112 may be perpendicular to the direction of currentflow.

Thus, forming the memory cell 101 may include forming the firstdielectric material 108 over the first electrode 106, forming thethreshold switching material 110 over the first dielectric material 108,and forming the second dielectric material 112 between the thresholdswitching material 110 and the second electrode 114.

The second electrode 114 may overlie the second dielectric material 112.In some embodiments, the second electrode 114 directly overlies andcontacts the second dielectric material 112. The second electrode 114may be configured to conduct current to the memory material 116. Thesecond electrode 114 may be formed from the same materials or fromdifferent materials as the first electrode 106. The second electrode 114may be formed from one of the materials described above for the firstelectrode 106. The second electrode 114 may include a carbon material ora conductive carbon-containing material. For example, the secondelectrode 114 may include a compound having carbon atoms, a carbonnitride, a carbon-containing metal silicide, a metal, or a metalnitride, as described above with reference to the first electrode 106.By way of non-limiting example, the second electrode may includeTiC_(x)N_(y), TaC_(x)N_(y), TiSiC_(x)N_(y), TiAlC_(x)N_(y),TiSiAlC_(x)N_(y), WC_(x)N_(y), TaCO_(x)N_(y), WSiC_(x)N_(y), W, Ti, Pt,Ru, RuO_(x), WN_(x), TiN_(x), TaN_(x), TiAl_(x)N_(y), and combinationsthereof, wherein x is between about 0 and about 6.0 and y is betweenabout 0 and about 6.0. In some embodiments, the second electrode 114includes the same material as the first electrode 106. In someembodiments, the second electrode 114 is a carbon electrode.

Similar to the first electrode 106 previously described, a thickness ofthe second electrode 114 may be selected at least partially based onmaterial characteristics of at least one other component of the memorycell 101. For example, the thickness of the second electrode 114 mayenable a threshold voltage of the second electrode 114 (e.g., a voltageat which the second electrode 114 functions as a low resistanceconductor) to be substantially close to a threshold voltage of thememory material 116. The thickness of the second electrode 114 may bebetween about 30 Å and about 2,000 Å, such as between about 100 Å andabout 1,500 Å. In at least some embodiments, the thickness of the secondelectrode 114 is about 2,000 Å. The thickness of the second electrode114 may be greater than, less than, or equal to the thickness of thefirst electrode 106.

The second electrode 114 may be formed by conventional techniquesincluding, but not limited to, ALD, CVD, PECVD, LPCVD, or PVD. Thesecond electrode 114 may be formed in a manner substantially similar tothat described above with respect to forming the first electrode 106.

The memory material 116 may be any known material (e.g., a programmablematerial) configured to be electrically switched or changed (i.e.,configured to reversibly electrically switch or change) between a firstphase and a second phase, where the first phase and the second phasediffer in at least one detectable (e.g., measurable) property (e.g.,electrical resistivity, electrical conductivity, optical transmissivity,optical absorption, optical refraction, optical reflectivity,morphology, surface topography, relative degree of order, relativedegree of disorder, or combinations thereof). For example, each physicalstate of the memory material 116 may exhibit a particular resistancethat may be used to distinguish logic values of the memory cell 101.

The memory material 116 may be formed between the second electrode 114and the third electrode 118. The memory material 116 may include astorage material suitable for a resistive-type memory cell (RRAM), suchas a dynamic random-access memory (DRAM) cell, a phase-change RAM(PCRAM) cell, a conductive-bridge RAM cell, a ferroelectric RAM (FRAM)cell, and a spin-transfer torque RAM (STTRAM) cell. The memory material116 may include a transition metal oxide, transition metals, alkalineearth metals, rare earth metals, and combinations thereof. Other memorymaterials 116 may include chalcogenides, binary metal oxides, colossalmagnetoresistive materials, polymer-based resistive materials, andcombinations thereof. In some embodiments, the memory material 116 is acompound including a chalcogenide and the threshold switching material110 is a different compound including the same or differentchalcogenides than the memory material 116.

The memory material 116 may be forming over the second electrode 114.The memory material 116 may be formed using conventional techniques,such as ALD, CVD, PECVD, LPCVD, and PVD, which are not described indetail herein.

The third electrode 118 may overlie the memory material 116. The thirdelectrode 118 may directly overlie and contact the memory material 116and may be configured to conduct current to the digit line 120 overlyingthe third electrode 118. The third electrode 118 may be formed from oneof the materials described above for the first electrode 106 and thesecond electrode 114. By way of example only, the third electrode 118may be formed from a compound having carbon atoms, a carbon nitride, acarbon containing metal silicide, a metal, or a metal nitride, asdescribed above with reference to the first electrode 106 and the secondelectrode 114. By way of non-limiting example, the second electrode mayinclude TiC_(x)N_(y), TaC_(x)N_(y), TiSiC_(x)N_(y), TiAlC_(x)N_(y),TiSiAlC_(x)N_(y), WC_(x)N_(y), TaCO_(x)N_(y), WSiC_(x)N_(y), W, Ti, Pt,Ru, RuO_(x), WN_(x), TiN_(x), TaN_(x), TiAl_(x)N_(y), and combinationsthereof, wherein x is between about 0 and about 6.0 and y is betweenabout 0 and about 6.0. In some embodiments, the third electrode 118 isformed from the same material as at least one of the first electrode 106and the second electrode 114. In some embodiments, the third electrode118 is a carbon electrode.

Similar to the first electrode 106 and the second electrode 114previously described, a thickness of the third electrode 118 may beselected at least partially based on material characteristics of atleast one other component of the memory cell 101. For example, thethickness of the third electrode 118 may enable a threshold voltage ofthe third electrode 118 (e.g., a voltage at which the third electrode118 functions as a low resistance conductor) to be substantially closeto a threshold voltage of the digit line 120. The thickness of the thirdelectrode 118 may be between about 30 Å and about 2,000 Å, such asbetween about 100 Å and about 1,500 Å. In at least some embodiments, thethickness of the third electrode 118 is about 2,000 Å. The thickness ofthe third electrode 118 may be greater than, less than, or equal to thethickness of the first electrode 16 or the thickness of the secondelectrode 114.

The third electrode 118 may be formed by conventional techniquesincluding, but not limited to, ALD, CVD, PECVD, LPCVD, or PVD. The thirdelectrode 118 may be formed in a manner substantially similar to thatdescribed above with respect to forming the first electrode 106 and thesecond electrode 114.

The digit line 120 may be formed from any suitable conductive materialincluding, but not limited to, a metal, a metal alloy, a conductivemetal oxide, or combinations thereof. By way of non-limiting example,the digit line 120 may be formed from W, WN, Ni, TaN, Pt, Au, TiN,TiSiN, TiAlN, or MoN. The digit line 120 may be formed fromsubstantially the same material as the word line 104 or may be formedfrom a different material than the word line 104. In at least someembodiments, the digit line 120 is formed from tungsten. The digit line120 may be formed on the third electrode 118 using conventionaltechniques, such as ALD, CVD, PECVD, LPCVD, or PVD, which are notdescribed in detail herein.

In further embodiments, relative positions of the threshold switchingmaterial 110 and the memory material 116 may be different than describedabove. For example, referring to FIG. 1B, a memory cell 101′ may includeeach component of memory cell 101 (FIG. 1A) previously described, exceptthat the relative positions of the threshold switching material 110′ andthe memory material 116′ may be switched (e.g., reversed). Thus, thememory cell 101′ may include, from bottom to top, the first electrode106, the memory material 116′, the second electrode 114, the firstdielectric material 108, the threshold switching material 110′, thesecond dielectric material 112, and the third electrode 118. The firstelectrode 106 may be formed on the word line 104, the memory material116′ may be formed on the first electrode 106, the second electrode 114may be formed on the memory material 116′, the first dielectric material108 may be formed on the second electrode 114, the threshold switchingmaterial 110′ may be formed on the first dielectric material 108, thesecond dielectric material 112 may be formed on the threshold switchingmaterial 110′, and the third electrode 118 may be formed on the seconddielectric material 112.

Accordingly, a memory cell is disclosed. The memory cell comprises athreshold switching material over a first electrode comprising carbon ona substrate, a second electrode over the threshold switching material,at least one dielectric material between the threshold switchingmaterial and at least one of the first electrode and the secondelectrode, and a memory material over the second electrode.

Accordingly, a method of forming a memory cell is disclosed. The methodcomprises forming a threshold switching material over a first electrodeon a substrate, forming a second electrode over the threshold switchingmaterial, forming a dielectric material between the threshold switchingmaterial and at least one of the first electrode and the secondelectrode, and forming a memory material over the second electrode.

Referring to FIG. 2A and FIG. 2B, a memory cell 102, 102′ may includecomponents similar to components of the memory cell 101 (FIG. 1A)previously described, except that only one of the first dielectricmaterial 108 and the second dielectric material 112 is present. Thefirst dielectric material 108 or the second dielectric material 112 maybe present on one side of the threshold switching material 110, such asbetween the threshold switching material 110 and the first electrode 106or between the threshold switching material 110 and the second electrode114.

Referring to FIG. 2A, the memory cell 102 includes the thresholdswitching material 110 between the first electrode 106 and the secondelectrode 114. The first dielectric material 108 may intervene betweenthe first electrode 106 and the threshold switching material 110. Thethreshold switching material 110 may directly overlie and contact thefirst dielectric material 108. The second electrode 114 may directlyoverlie and contact the threshold switching material 110.

Referring to FIG. 2B, the memory cell 102′ includes the thresholdswitching material 110 between the first electrode 106 and the secondelectrode 114. The threshold switching material 110 may directly overlieand contact the first electrode 106. The second dielectric material 112may directly overlie and contact the threshold switching material 110.The second dielectric material 112 may intervene between the thresholdswitching material 110 and the second electrode 114.

The materials of the first electrode 106, the first dielectric material108, the threshold switching material 110, the second electrode 114, thememory material 116, and the third electrode 118 may be substantiallysimilar to those described above and may be formed in a substantiallysimilar manner as described above.

Referring to FIG. 3A, another embodiment of a memory cell 103 is shown.The memory cell 103 includes components similar to components of thememory cell 101′ (FIG. 1B) previously described, except that the seconddielectric material 112 is not present. Thus, the memory cell 103includes, from bottom to top, the first electrode 106, the memorymaterial 116′, the second electrode 114, the first dielectric material108, the threshold switching material 110′, and the third electrode 118.The first dielectric material 108 intervenes between the secondelectrode 114 and the threshold switching material 110′. The firstdielectric material 108 may directly overlie and contact the secondelectrode 114. The threshold switching material 110′ may directlyoverlie and contact the first dielectric material 108. The thirdelectrode 118 may directly overlie and contact the threshold switchingmaterial 110′.

Referring to FIG. 3B, another embodiment of a memory cell 103′ is shown.The memory cell 103′ includes components similar to components of thememory cell 103 (FIG. 3A) previously described, except that the firstdielectric material 108 (FIG. 3A) is not present and the seconddielectric material 112 intervenes between the threshold switchingmaterial 110′ and the third electrode 118. Thus, the memory cell 103′includes, from bottom to top, the first electrode 106, the memorymaterial 116′, the second electrode 114, the threshold switchingmaterial 110′, the second dielectric material 112, and the thirdelectrode 118. The threshold switching material 110′ may directlyoverlie and contact the second electrode 114. The second dielectricmaterial 112 may directly overlie and contact the threshold switchingmaterial 110′. The third electrode 118 may directly overlie and contactthe second dielectric material 112.

Accordingly, a memory cell comprising one intervening dielectricmaterial between an electrode and a threshold switching material isdisclosed. The memory cell comprises a threshold switching materialbetween a pair of electrodes, at least one dielectric material betweenthe threshold switching material and at least one electrode of the pairof electrodes, and a memory material adjacent at least one of theelectrodes of the pair of electrodes.

Referring to FIG. 4, another embodiment of a memory cell 150 is shown.The memory cell 150 includes components similar to components of thememory cell 101 (FIG. 1A) previously described, except that firstelectrode 106′, second electrode 114′, third electrode 118′, andthreshold switching material 110″ may be formed from differentmaterials. Thus, the memory cell 150 includes, from bottom to top, thefirst electrode 106′, the first dielectric material 108, the thresholdswitching material 110″, the second dielectric material 112, the secondelectrode 114′, the memory material 116, and the third electrode 118′.

The first electrode 106′, the second electrode 114′, and the thirdelectrode 118′ may each be formed of a conductive material. Theelectrodes may be formed from a metal, a metal silicide, or polysilicon.For example, the electrodes may be formed from polysilicon, tungsten,platinum, palladium, tantalum, nickel, titanium nitride, tantalumnitride, tungsten nitride, tungsten silicide (WSi_(x)), cobalt silicide(CoSi_(x)), tantalum silicide (TaSi_(x)), manganese silicide (MnSi_(x)),ruthenium silicide (RuSi_(x)), and nickel silicide (NiSi_(x)), (whereinx is a rational number greater than zero), or combinations thereof. Insome embodiments, the first electrode 106′, the second electrode 114′,and the third electrode 118′ are formed from a metal material. Each ofthe first electrode 106′, the second electrode 114′, and the thirdelectrode 118′ may be formed from the same material or differentmaterials as at least one of the other of the first electrode 106′, thesecond electrode 114′, and the third electrode 118′. Each of the firstelectrode 106′, the second electrode 114′, and the third electrode 118′may be formed as described above with reference to the first electrode106, the second electrode 114, and the third electrode 118 of FIG. 1A.The first electrode 106′, the second electrode 114′, and the thirdelectrode 118′ may be formed by conventional techniques including, butnot limited to, ALD, CVD, PECVD, LPCVD, and PVD. The thickness of eachof the first electrode 106′, the second electrode 114′, and the thirdelectrode 118′ may be between about 100 Å and about 2,000 Å, such asbetween about 300 Å and about 1,500 Å.

The threshold switching material 110″ may be formed from amorphoussilicon. The amorphous silicon may be substantially pure. The amorphoussilicon may have a concentration of silicon between about 90 atomicpercent and about 100 atomic percent. In some embodiments, the thresholdswitching material 110″ is homogeneous and includes about 100 atomicpercent amorphous silicon. The threshold switching material 110″ mayalso include amorphous silicon doped with one or more materials. Thethreshold switching material 110″ may include amorphous silicon dopedwith p-type dopants (e.g., boron atoms, aluminum atoms, or galliumatoms), or n-type dopants (e.g., phosphorus atoms or nitrogen atoms). Insome embodiments, the amorphous silicon may be doped with dopants thatincrease a crystallization temperature of the amorphous silicon, such asat least one of carbon, oxygen, and nitrogen. In other embodiments, thethreshold switching material 110″ includes amorphous silicon and betweenabout 1 atomic percent and about 30 atomic percent of at least one ofcarbon, oxygen, and nitrogen.

The threshold switching material 110″ may be formed using conventionaltechniques, such as ALD, CVD, PECVD, LPCVD, or PVD, which are notdescribed in detail herein.

The first dielectric material 108 may intervene between the firstelectrode 106′ and the threshold switching material 110″. The firstdielectric material 108 may directly contact each of the first electrode106′ and the threshold switching material 110″. The first dielectricmaterial 108 may form a continuous material between the first electrode106′ and the threshold switching material 110″ such that the firstelectrode 106′ is physically isolated from the threshold switchingmaterial 110″. However, the first dielectric material 108 may bediscontinuous as long as the first electrode 106′ does not physicallycontact the threshold switching material 110″. In some embodiments, thefirst dielectric material 108 is in direct contact with the thresholdswitching material 110″ and another material (not shown) intervenesbetween the first dielectric material 108 and the first electrode 106′.In some embodiments, the first dielectric material 108 is TiO₂.

The second dielectric material 112 may overlie the threshold switchingmaterial 110″. The second dielectric material 112 may intervene betweenthe threshold switching material 110″ and the second electrode 114′. Thesecond dielectric material 112 may directly contact each of thethreshold switching material 110″ and the second electrode 114′. Thesecond dielectric material 112 may form a continuous material betweenthe threshold switching material 110″ and the second electrode 114′ suchthat the threshold switching material 110″ is physically isolated fromthe second electrode 114′. However, the second dielectric material 112may be discontinuous as long as the second electrode 114′ does notphysically contact the threshold switching material 110″. In someembodiments, the second dielectric material 112 is in direct contactwith the threshold switching material 110″ and another material (notshown) intervenes between the second dielectric material 112 and thesecond electrode 114′. In some embodiments, the second dielectricmaterial 112 is TiO₂.

Referring to FIG. 5, yet another embodiment of a memory cell 151including a dielectric material in contact with one electrode and thethreshold switching material 110″ is shown. The memory cell 151 includescomponents similar to components of the memory cell 150 (FIG. 4)previously described, except that the second dielectric material 112 isnot present. Thus, the memory cell 151 includes, from bottom to top, thefirst electrode 106′, the first dielectric material 108, the thresholdswitching material 110″, the second electrode 114′, the memory material116, and the third electrode 118′. The first dielectric material 108intervenes between the first electrode 106′ and the threshold switchingmaterial 110″. The first dielectric material 108 may overlie the firstelectrode 106′ and directly contact the threshold switching material110″.

Referring to FIG. 6, another embodiment of a memory cell 152 is shown.The memory cell 152 includes components similar to components of thememory cell 150 (FIG. 4) previously described, except that the firstdielectric material 108 is not present. Thus, the memory cell 152includes, from bottom to top, the first electrode 106′, the thresholdswitching material 110″, the second dielectric material 112, the secondelectrode 114′, the memory material 116, and the third electrode 118′.The second dielectric material 112 intervenes between the thresholdswitching material 110″ and the second electrode 114′. The seconddielectric material 112 may directly overlie and contact the thresholdswitching material 110″.

The materials of the first dielectric material 108, the seconddielectric material 112, and the memory material 116 may besubstantially similar to those described above and may be formed in asubstantially similar manner as described above.

In further embodiments, relative positions of the threshold switchingmaterial 110″ and the memory material 116 may be different thandescribed above in each of FIG. 4 through FIG. 6. For example, in eachof FIG. 4 through FIG. 6, the relative position of the thresholdswitching material 110″ may be reversed with the position of the memorymaterial 116. Each of the first dielectric material 108 and the seconddielectric material 112 may remain in contact with the thresholdswitching material 110″, as described above.

Referring to FIG. 7, a memory array 200 including a plurality of memorycells 202 is shown. The memory cells 202 may be one of the memory cells101, 101′, 102, 102′, 103, 103′, 150, 151, 152 previously described. Theplurality of memory cells 202 may be positioned between a plurality ofword lines 204 and a plurality of digit lines 220. The plurality of wordlines 204 may correspond to one of the word lines 104 previouslydescribed and the plurality of digit lines 220 may correspond to one ofthe digit lines 120 previously described. Each of the word lines 204 mayextend in a first direction and may connect to a row of the memory cells202. Each of the digit lines 220 may extend in a second direction atleast substantially perpendicular to the first direction and may connectto a column of the memory cells 202. Each of the memory cells 202 mayinclude a word line node (not shown) coupled to a respective word line204, and a digit line node (not shown) coupled to a respective digitline 220. A voltage applied to the word lines 204 and the digit lines220 may be controlled such that an electric field may be selectivelyapplied to at least one word line 204 and to at least one digit line220, enabling the memory cells 202 to be selectively operated.Accordingly, a memory device may be formed which includes the memoryarray 200.

FIG. 8 illustrates a memory device 300 that includes the memory array200 (FIG. 7) including the plurality of memory cells 202, the pluralityof word lines 204, the plurality of digit lines 220, an insulatormaterial 222, a first insulating dielectric material 224, and anoptional second insulating dielectric material 226. Each of theinsulator material 222, the first insulating dielectric material 224,and the optional second insulating dielectric material 226 may be asuitable insulative or dielectric material including, but not limitedto, silicon oxide, silicon nitride, silicon oxynitride, a spin-on-glass(SOG), a phosphosilicate glass (PSG), tetraethyl orthosilicate (TEOS),or borophosilicate glass (BPSG). The memory device 300 may be formed byconventional techniques.

Accordingly, a memory device comprises word lines over a substrate,digit lines perpendicular to the word lines, and memory cells arrangedin an array of rows and columns, each memory cell coupled to arespective word line and coupled to a respective digit line andcomprising a threshold switching material over a first electrode on asubstrate, a second electrode over the threshold switching material, adielectric material between the threshold switching material and atleast one of the first electrode and the second electrode, and a memorymaterial over the second electrode.

Referring to FIG. 9A through FIG. 9E, a method of forming the memorydevice 300 (FIG. 8) is described. By way of non-limiting example and asillustrated in FIG. 9A, the plurality of word lines 204 may be formed inthe insulator material 222. As shown in FIG. 9B, a memory cell 202′ maybe formed on the plurality of word lines 204 and the insulator material222 in a manner substantially similar to that previously described forone of the memory cells 101, 101′, 102, 102′, 103, 103′, 150, 151, and152. For example, a first electrode 206 may be formed over the wordlines 204 and insulator material 222, a first dielectric material 208may be formed over the first electrode 206, a threshold switchingmaterial 210 may be formed over the first dielectric material 208, asecond dielectric material 212 may be formed over the thresholdswitching material 210, a middle electrode 214 may be formed over thesecond dielectric material 212, a memory material 216 may be formed overthe middle electrode 214, and a third electrode 218 may be formed overthe memory material 216. As illustrated in FIG. 9C, openings 230 may beformed in a hardmask 228 overlying the memory cell 202′. The openings230 may be used as a mask to transfer a corresponding pattern into thememory cell 202′ to form the plurality of memory cells 202 and theopenings 230′, as shown in FIG. 9D. Remaining portions of the hardmask228 may be removed (e.g., by etching or chemical mechanicalplanarization). The first insulating dielectric material 224 mayoptionally be formed over the plurality of memory cells 202 and theplurality of openings 230′ may be filled with the optional secondinsulating dielectric material 226. A portion of at least one of thefirst insulating dielectric material 224, the second insulatingdielectric material 226, and the plurality of memory cells 202 may beremoved (e.g., by chemical mechanical planarization) to form asubstantially planar surface 232, as shown in FIG. 9E. The plurality ofdigit lines 220 may then be formed on the substantially planar surface232 using conventional techniques to form the memory device 300illustrated in FIG. 8.

In use and operation, the word lines 204 and the digit lines 220 of thememory device 300 are connected to circuitry (not shown) configured toprogram and read the memory device 300. Current delivered to theplurality of word lines 204 (e.g., by electrical contact with aninterconnect) may flow through the plurality of memory cells 202, and tothe plurality of digit lines 220. By way of non-limiting example andreferring to FIG. 1A, if the plurality of memory cells 202 (FIG. 8) arethe memory cells 101, described above, current from the plurality ofword lines 204 may flow through the first electrode 106, the firstdielectric material 108, the threshold switching material 110, thesecond dielectric material 112, the second electrode 114, the memorymaterial 116, and the third electrode 118, to the digit lines 120 (FIG.8). As the current passes through the memory material 116, at least onedetectable property change (e.g., an electrical resistivity change, asdescribed above) may occur and be utilized to distinguish logic valuesof the memory cell 101 as desired. If the plurality of memory cells 202(FIG. 8) include one of the other memory cells 101′, 102, 102′, 103,103′, 150, 151, 152 the memory device 300 may be used and operated in asimilar manner.

The memory cells 101, 101′, 102, 102′, 103, 103′, 150, 151, 152 andmemory device 300 advantageously reduce energy demands, increase memorylifespan, and decrease performance degradation issues as compared toconventional memory cells and devices. For example, the presence of atleast one of the first dielectric material 108 and the second dielectricmaterial 112 in the memory cells 101, 101′, 102, 102′, 103, 103′, 150,151, 152 and memory device 300 reduce electrical defects at theinterface between the threshold switching material 110 and materialsadjacent the threshold switching material 110, 110′, 110″. As a result,the memory cells exhibit a lower variability in contact resistance, andan associated lower variability in threshold voltage in each memory cellof the array. In addition, each memory cell exhibits a lower currentleakage when the threshold switching material 110, 110′, 110″ is in theoff state. Providing at least one of the first dielectric material 108and the second dielectric material 112 on at least one of opposing sidesof the threshold switching material 110, 110′, 110″ of the memory cells101, 101′, 102, 102′, 103, 103′, 150, 151, 152 may also increase thestability of the cells through a higher number of operation cycles ascompared to conventional memory cells.

In addition, the presence of at least one of the first dielectricmaterial 108 and the second dielectric material 112 enable a broaderrange of materials to be used as the electrodes of the memory cells 101,101′, 102, 102′, 103, 103′, 150, 151, 152. The electrodes may beselected based on the desired work function of the electrode, ratherthan selecting the material of the electrodes to be substantiallynonreactive with the threshold switching material 110, 110′, 110″.

EXAMPLES Example 1

FIG. 10 is a graphical representation of the threshold voltagedistribution of a memory cell array having memory cells includingintervening dielectric materials between a threshold switching materialand adjacent electrodes compared to a threshold voltage distribution ofa conventional memory cell array. A 10 Å Al₂O₃ dielectric material wasformed over a 100 Å carbon containing electrode. An approximately 120 Åthick chalcogenide threshold switching material including germanium,selenium, and arsenic atoms was formed over the Al₂O₃ dielectricmaterial. Another 10 Å Al₂O₃ dielectric material was forming over thechalcogenide threshold switching material. Another 100 Å carboncontaining electrode was formed over the Al₂O₃ dielectric material. Thethreshold voltage of the memory cells including the interveningdielectric materials exhibited a generally lower threshold voltage and atighter distribution of threshold voltages compared to the conventionalmemory cells that lack the dielectric materials between the thresholdswitching material and electrodes. The threshold voltage of the eachmemory cell in the memory array was closer to the average thresholdvoltage of the plurality of memory cells in the memory array than inconventional memory cell arrays (i.e., the threshold voltage of eachmemory cell within the memory array including the dielectric materialsbetween the threshold switching material and the electrodes have asmaller standard deviation than conventional memory cells that lack thedielectric materials). The standard deviation of the threshold voltageof the memory cells including the intervening dielectric is reducedcompared to a standard deviation of the threshold voltage of memorycells in a conventional memory cell.

The leakage current of the memory cells including the interveningdielectric materials remained stable after several on/off cycles werebeen performed at different leakage current densities. Afterapproximately 1e6 (one million) on/off cycles, the memory cells remainedstable without an increased amount of current leaking through the memorycells. The memory cells remained stable through a wide range of pulsingwidths with each pulse width ranging from about milliseconds to aboutnanoseconds and over a wide range of current pulses through the memorycells.

Example 2

Referring to FIG. 11A through FIG. 11C, graphical representations of theleakage current of a memory cell including an intervening dielectricmaterial between a threshold switching material and an electrode isshown and compared to a conventional memory cell lacking the interveningdielectric material. The conventional memory cell is shown in a brokenline and the memory cell including the intervening dielectric materialis shown as a solid line. A 10 Å TiO₂ dielectric material was formedover a metal electrode. An amorphous silicon threshold switchingmaterial was formed over the TiO₂ dielectric material. Another electrodewas formed over the amorphous silicon threshold switching material.Referring to FIG. 11A, the leakage current of the memory cells includingthe TiO₂ dielectric material was about the same as that of aconventional memory cell in the first cycle. Referring to FIG. 11B andFIG. 11C, during the second cycle and the tenth cycle, respectively, theleakage current through the memory cell including the TiO₂ dielectricmaterial was lower than the leakage current through the conventionalmemory cell. Referring to FIG. 11D, the memory cell including the TiO₂dielectric material had a reduced leakage voltage compared to theconventional memory cell. The memory cells including the TiO₂ dielectricmaterial were stable after a high number of cycles (e.g., about onemillion cycles) over a broad range of pulsing widths. The memory cellsincluding the TiO₂ dielectric material were more stable than theconventional memory cells, particularly after a higher number of cyclesand at greater pulse widths.

While certain illustrative embodiments have been described in connectionwith the figures, those of ordinary skill in the art will recognize andappreciate that embodiments encompassed by the disclosure are notlimited to those embodiments explicitly shown and described herein.Rather, additions, deletions, and modifications to the embodimentsdescribed herein may be made without departing from the scope ofembodiments encompassed by the disclosure, such as those hereinafterclaimed, including legal equivalents. In addition, features from onedisclosed embodiment may be combined with features of another disclosedembodiment while still being encompassed within the scope of thedisclosure as contemplated by the inventors.

What is claimed is:
 1. A memory cell, comprising: a threshold switchingmaterial comprising amorphous silicon and at least one of carbon,oxygen, or nitrogen between a pair of electrodes, wherein each electrodeof the pair of electrodes comprises polysilicon, tungsten, platinum,palladium, tantalum, nickel, tantalum nitride, tungsten nitride, a metalsilicide, or combinations thereof; at least one doped dielectricmaterial between the threshold switching material and at least oneelectrode of the pair of electrodes, the threshold switching materialover the at least one doped dielectric material; and a memory materialadjacent at least one of the electrodes of the pair of electrodes. 2.The memory cell of claim 1, wherein the each electrode of the pair ofelectrodes comprises the same material.
 3. The memory cell of claim 1,wherein the at least one doped dielectric material comprises aluminumoxide.
 4. The memory cell of claim 1, wherein the at least one electrodeof the pair of electrodes comprises a metal material in contact with theat least one doped dielectric material.
 5. The memory cell of claim 1,further comprising another dielectric material overlying the thresholdswitching material.
 6. The memory cell of claim 1, further comprisinganother electrode on a side of the memory material opposite the at leastone electrode of the pair of electrodes.
 7. The memory cell of claim 1,wherein the at least one dielectric material between the thresholdswitching material and at least one electrode of the pair of electrodesis in direct contact with the threshold switching material.
 8. A memorycell, comprising: a threshold switching material over a first electrodecomprising carbon on a substrate; a second electrode over the thresholdswitching material; at least one dielectric material between thethreshold switching material and at least one of the first electrode orthe second electrode, wherein at least a portion of the at least onedielectric material is doped; and a memory material over the secondelectrode.
 9. The memory cell of claim 8, wherein the thresholdswitching material comprises a chalcogenide material.
 10. The memorycell of claim 8, wherein the threshold switching material comprisesarsenic, selenium, silicon, and germanium.
 11. The memory cell of claim8, wherein the at least one dielectric material comprises aluminumoxide, aluminum silicon oxide, strontium oxide, barium oxide, strontiumtitanium oxide, magnesium oxide, a refractory metal oxide, a refractorymetal alloy oxide, or combinations thereof.
 12. The memory cell of claim8, wherein the at least one dielectric material has a thickness ofbetween about 3 Å and about 50 Å.
 13. The memory cell of claim 8,wherein the at least one dielectric material is between the thresholdswitching material and the first electrode.
 14. The memory cell of claim8, wherein the at least one dielectric material is between the thresholdswitching material and the second electrode.
 15. The memory cell ofclaim 8, wherein a first dielectric material of the at least onedielectric material is between the threshold switching material and thefirst electrode and a second dielectric material of the at least onedielectric material is between the threshold switching material and thesecond electrode.
 16. A method of forming a memory cell, the methodcomprising: forming a threshold switching material over a firstelectrode comprising carbon on a substrate; forming a second electrodeover the threshold switching material; forming a dielectric materialbetween the threshold switching material and at least one of the firstelectrode or the second electrode; doping at least a portion of thedielectric material; and forming a memory material over the secondelectrode.
 17. The method of claim 16, wherein forming a thresholdswitching material over a first electrode comprising carbon on asubstrate comprises forming the threshold switching material comprisinga chalcogenide material over the first electrode.
 18. The method ofclaim 16, wherein forming a threshold switching material over a firstelectrode comprising carbon on a substrate comprises forming thethreshold switching material without substantially reacting thethreshold switching material with the first electrode.
 19. The method ofclaim 16, wherein forming a second electrode comprises forming thesecond electrode from the same material as the first electrode.
 20. Themethod of claim 16, wherein forming a dielectric material between thethreshold switching material and at least one of the first electrode orthe second electrode comprises at least one of: forming a firstdielectric material between the threshold switching material and thefirst electrode; and forming a second dielectric material between thethreshold switching material and the second electrode.
 21. The method ofclaim 16, wherein forming a dielectric material comprises formingbetween about 3 Å and about 50 Å of the dielectric material in contactwith the threshold switching material.
 22. The method of claim 16,wherein forming a dielectric material comprises forming a dielectricmaterial comprising aluminum oxide, aluminum silicon oxide, strontiumoxide, barium oxide, strontium titanium oxide, magnesium oxide, arefractory metal oxide, a refractory metal alloy oxide, or combinationsthereof.
 23. The memory cell of claim 1, wherein a thickness of the atleast one doped dielectric material is between about 3 Å and about 5 Å.24. The memory cell of claim 1, wherein the threshold switching materialis doped with at least one of boron, aluminum, gallium, or phosphorus.25. The memory cell of claim 1, wherein the at least one dopeddielectric material is doped with oxygen, sulfur, carbon, fluorine, ametallic element, or combinations thereof.
 26. The memory cell of claim1, wherein the at least one doped dielectric material is between thethreshold switching material and one electrode of the pair ofelectrodes, the other electrode of the pair of electrodes in directcontact with the threshold switching material.
 27. The memory cell ofclaim 1, wherein the at least one doped dielectric material comprisesaluminum silicon oxide, strontium oxide, barium oxide, strontiumtitanium oxide, or combinations thereof.